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--连接数据库时，host和user的匹配规则
官方文档：https://dev.mysql.com/doc/refman/5.7/en/connection-access.html
--host和user的匹配规则如下：
--是host为明确的最先匹配，host带%模糊的时候最后匹配，但host为''(空)位于%之后才匹配
--相同的host时候，比较user为明确的最先匹配，user为''(空)最后匹配
--相同的host和user时，排序是不确定的
When multiple matches are possible, the server must determine which of them to use. It resolves this issue as follows:
Whenever the server reads the user table into memory, it sorts the rows.
When a client attempts to connect, the server looks through the rows in sorted order.
The server uses the first row that matches the client host name and user name.
The server uses sorting rules that order rows with the most-specific Host values first. Literal host names and IP addresses are the most specific. (The specificity of a literal IP address is not affected by whether it has a netmask, so 198.51.100.13 and 198.51.100.0/255.255.255.0 are considered equally specific.) The pattern '%' means “any host” and is least specific. The empty string '' also means “any host” but sorts after '%'. Rows with the same Host value are ordered with the most-specific User values first (a blank User value means “any user” and is least specific). For rows with equally-specific Host and User values, the order is nondeterministic.
--查看当前的host及用户信息匹配顺序，先host顺序匹配、后user顺序匹配
mysql> SELECT authentication_string, host, user,account_locked FROM mysql.USER ORDER BY host desc ,user desc;
+-------------------------------------------+--------------+---------------+----------------+
| authentication_string | host | user | account_locked |
+-------------------------------------------+--------------+---------------+----------------+
| *511C0A408C5065XXEC90D60YYA1AB9437281AF28 | localhost | root | N |
| *THISISNOTAVALIXXASSWORDYYATCANBEUSEDHERE | localhost | mysql.sys | Y |
| *THISISNOTAVALIXXASSWORDYYATCANBEUSEDHERE | localhost | mysql.session | Y |
| *485CE31BA547A4XXC047659YY10DF200F361CD4E | localhost | bkpuser | N |
| *7B502777D8FF69XX4B56BC2YY2867F4B47321BA8 | 192.168.56.% | repl | N |
| *AECCE73463829AXX3968838YYF6F85E43C3F169C | % | flyremote | N |
| *566AC8467DAAAEXXE247AE7YY0A770E9B97D9FB0 | | flylocal | N |
+-------------------------------------------+--------------+---------------+----------------+
8 rows in set (0.00 sec)
--举个特殊例子
--建立两个特殊用户如下，一个用户名为''(空)、一个用户名和host都为''(空)
mysql> create user ''@'localhost' identified by "Kong123$";
Query OK, 0 rows affected (0.00 sec)
mysql> create user ''@'' identified by "doubleKong123$";
Query OK, 0 rows affected (0.00 sec)
--查看当前的host及用户信息匹配顺序，先host顺序匹配、后user顺序匹配
mysql> SELECT authentication_string, host, user,account_locked FROM mysql.USER ORDER BY host desc ,user desc;
+-------------------------------------------+--------------+---------------+----------------+
| authentication_string | host | user | account_locked |
+-------------------------------------------+--------------+---------------+----------------+
| *511C0VVV8C5065CBEC90D6TTTT1AB9437281AF28 | localhost | root | N |
| *THISIVVVTAVALIDPASSWORTTTTTCANBEUSEDHERE | localhost | mysql.sys | Y |
| *THISIVVVTAVALIDPASSWORTTTTTCANBEUSEDHERE | localhost | mysql.session | Y |
| *485CEVVVA547A48CC04765TTTT0DF200F361CD4E | localhost | bkpuser | N |
| *256D7VVV91F7363EBDADEFTTTTB74B2B318746FC | localhost | | N |
| *7B502VVVD8FF69164B56BCTTTT867F4B47321BA8 | 192.168.56.% | repl | N |
| *AECCEVVV63829A5F396883TTTT6F85E43C3F169C | % | flyremote | N |
| *566ACVVV7DAAAE79E247AETTTTA770E9B97D9FB0 | | flylocal | N |
| *AE162VVV68403D1D98A4C9TTTT50A508B8C56F3F | | | N |
+-------------------------------------------+--------------+---------------+----------------+
9 rows in set (0.00 sec)
--这样本地登录flyremote用户时 会报错，因为按以上的顺序 优先匹配到了host为localhost、user为''(空)的用户，而不是flyremote用户 (因为user为''(空)的用户可以匹配任意用户名)
[root@hostmysql-m mysql]# mysql -uflyremote -pFlyremote123$
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1045 (28000): Access denied for user 'flyremote'@'localhost' (using password: YES)
--那就是说本地登录flyremote用户时， 用匹配到的host为localhost、user为''(空)的密码 Kong123$ ，就可以正常登陆了
[root@hostmysql-m mysql]# mysql -uflyremote -pKong123$
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your Mz>K | 
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